A method for receiving Doppler ultra sound signals at a high sample rate, at greater depths and from a large range gate size by increasing the length of time during which echoes can be received with respect to the time required to transmit the Doppler pulses that cause the echo signals to be created. According to a first embodiment of the invention, a Doppler pulse is transmitted for a time equal to the time required for an ultrasonic sound wave to travel from a transducer to a top of a range gate and back. Echo signals created in response to the long Doppler pulse are received for a time equal to the transmit time plus the time required for an ultrasonic sound wave to travel from the top of the range gate to a bottom of the range gate and back to the top of the range gate. In accordance with another aspect of the invention, each transducer element transmits a phase-shifted Doppler pulse, wherein the phase-shift is selected according to the time required for an ultrasonic sound wave to travel from the transducer element to a desired focal point. By simultaneously transmitting the phase-shifted Doppler pulses, the pulses arrive at different times at the focal point and constructively add. Echo signals created in response to the sum of the phase-shifted Doppler pulses can be sampled at substantially any rate to analyze the moving blood flow in the area of tissue defined by a range gat.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method of producing Doppler ultrasound data from an area of tissue defined by a range gate, comprising: transmitting a Doppler pulse having a duration substantially equal to the time required for an ultrasonic sound wave to travel from a transducer to a top of a range gate and back; receiving echo signals created in response to the Doppler pulse transmitted; sampling the received echo signals at a desired rate; and using the sampled echo signals to analyze moving blood flow in the area of tissue defined by the range gate.
2. The method of claim 1 , wherein the step of receiving Doppler echo signals comprises: receiving the echo signals for a period of time substantially equal to a time required for an ultrasonic sound wave to travel from the transducer to a bottom of the range gate and back.
3. A method of producing Doppler ultrasound data from an area of tissue defined by a range gate, comprising: determining a time required for an ultrasonic sound wave to travel between a number of individual transducer elements of an ultrasound transducer and a focal point of a Doppler pulse; shifting the phase of a Doppler pulse to be transmitted from each transducer element based on the times determined; simultaneously transmitting a phase-shifted Doppler pulse from each transducer element; and sampling echo signals created in the area of tissue defined by the range gate in response to the simultaneously transmitted, phase-shifted Doppler pulses.
4. The method of claim 3 , wherein the phase of the Doppler pulses is shifted such that the Doppler pulses add coherently in the area of tissue defined by the range gate.
5. A Doppler ultrasound system, comprising: a transducer that transmits Doppler pulses into tissue and generates electronic echo signals in response to received echoes; a transmit control that supplies the Doppler pulses to the transducer; a central processing unit that directs the transmit control to supply the Doppler pulses to the transducer such that a period of time during which the transducer receives the echoes responsive to a position shorter than the transmit time is greater than a period of time during which the transducer is transmitting Doppler pulses into the tissue; a digital beamformer controlled by the central processing unit that focuses the electronic echo signals received from an area of tissue defined by a range gate; and a Doppler processor that receives the focused echo signals and determines the direction and velocity of moving blood flow in the area of tissue defined by the range gate.
6. The Doppler ultrasound system of claim 5 , wherein the central processing unit increases the receive time of the echoes with respect to the transmit time of the Doppler pulses by: directing the transmit control to deliver a Doppler pulse to the transducer that has a duration substantially equal to the time required for an ultrasonic sound wave to travel from the transducer to a top of a range gate and back; and directing the digital beamformer to receive the electronic echo signals for a time substantially equal to the time required for an ultrasonic sound wave to travel from the transducer to a bottom of a range gate and back.
7. The Doppler ultrasound system of claim 5 , wherein the central processing unit increases the receive time of the echoes with respect to the transmit time of the Doppler pulses by: directing the transmit control to supply phase shifted Doppler pulses to a number of individual transducer elements for simultaneous transmission, wherein the phase shift of each Doppler pulse is determined by a transducer element's distance from the focal point of the Doppler pulses.
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April 27, 2000
June 25, 2002
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